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Can carbon fiber be threaded or machined??

grinch

Cast Iron
Joined
Feb 15, 2002
Location
Coronado CA
was wanting to incorperate some carbon fiber into a project im doing and was wondering if I could reliably thread it and screw in an aluminum piece.

Thanks
 
I will venture a complete guess that the answer is "no" not with much strength.

Couple observations...carbon fiber relies on the axial strength of the fibers and also the weave, which transmits the load to be shared by other fibers.

The crest of the thread, unless specifically molded or laid-up that way is just going to be a peak that is disjointed from the other fibers and relies largely on the strength of the matrix (epoxy?).

The threads I've seen integrated to carbon fiber were made in metal bosses for internal and with an external stud-projection.

However there's a lot I haven't seen!

-Matt
 
Matt has it right Grinch.

However, if you don't need the strength (which I doubt is the case, otherwise why carbon fibre?) you would need to mill or grind the threads. Grinding would be preferred.
 
As an aviation safety officer, I was taught to be VERY CAREFUL around crashes with airplanes that had carbon fiber parts, as the strands of fiber stuff could get into you, and you can't get them out. Crash scenes are first sprayed with something to encapsulate the stuff, then you can be around the site safely.

I would think machining the stuff might free up the fibers nearly the same? But of course I've seen knife handles made out of carbon graphite, so I don't really know, but it's worth looking into further if you're not sure either!

Tools
 
Grinch,

I'm not sure what would work, but there's some amazing adhesives that might effect your desired result. Between urethanes and 2 part epoxys, I bet there's something that'd work with a through or blind hole in the aluminum.

Kevin D.
 
Machining composites is fairly common. Typically, "sacrificial plies" are added so that there is material for machining. Theading on the other hand, isn't a good idea, however, bonding in a threaded insert would be a common practice.
 
Hello everyone...I work as a materials designer at a major university and build stuff out of carbon fiber material all the time and YES, you can machine carbon composites quite easily using carbide tooling or diamond tooling and machine while wet to prevent dust and contain the fine fibers. The best threads if internal would be made using a discontinuous fiber in a carbon or epoxy matrix and using a new, sharp tap as you would when tapping aluminum. Bonding inserts is another option. Best regards,Mark in Buffalo
 
Machining carbon fiber composites is commonplace in the industry I work in (military aerospace).

For graphite Reinforced composite materials, the term "machining" has been morphed with the term "routing". The process uses high spindle speeds (>15,000 rpm typically) and very expensive cutting tools, typically polycrystalline diamond.

Generally, the composite laminate has to be designed to take into account the machining process. Typically, in a location where a feature is being machined (such as a fuel access port in a composite wing skin), you place extra plies of "pad-up" material with multi-directional fiber orientations to bolster the interlaminar tension of the laminate stack in that area to resist fraying and delaminating as a result of the cutter forces. Machining processes are also used exteneively to edge trim a part after it has been molded and cured.


Its messy, expensive, but it is done all the time.


To answer your question.....No I would not reccommend threading a carbon fiber laminate directly. You will destroy the integrity of the laminate.

The best way to accomplish holes in composites is with molded-in inserts, or drill a hole after the fact and bond in an insert. Or use a through hole and a bonded nutplate on the backside.

-erik
 
I've done this with with CF/Graphite comp. about 3mm thick. However it was in hobby related project, not mission critical or human danger enabling application.

Clamping sacrificial aluminim plates on each side and drilling/tapping right through helps with fraying. I ended up bonding a stud to the threads, you could even go from the backside with a headless fastener. (or machine a screw/bolt head down just leaving a small shoulder )

I used a product called Gorilla Glue for the bond, sorry not very scientific but it worked.
 
Years ago one of my jobs was building the machines that made carbon fiber sheets. All of the relay/switch enclosures had to be able to be sealed to exclude the very conductive fibers that were generated during the manufacturing process. I recall having a low presssure filtered air system for the boxes that had controls in them.
 
hey thanks for all the great replys guys this is alot of great info.

can anyone recommend a good epoxy to bond in some threaded inserts?? Is they any that are good at handling heat?? temp range 250-300 F

Thanks
 








 
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